Rohit.. you are not required to use any promo code leave it blank and continue for the payment.
On payment page write down your debit card number and then click on check for offer.
If you are eligible for offer it will show Congratulations. Your ICICI card is eligible for cash back.
after that you can complete the transaction.

Mandatory things are:
a) promocode to be entered as your icici debitcard number
b) should use icici payment gateway
c) max cashback is of 250
d) where would we be getting this amount? on icici account or freecharge account???
SMI pls answer and add any other mandatory stuff to be followed quickly. thanks